I'm importing a model, and the whole model is joined. I'm trying to separate the model's parts
In order to seperate parts a mesh, go into edit mode on the object in question, then either right click and select seperate, open the quick search menu and type seperate, open the mesh menu in the top of the 3D viewport and select seperate, or use the hotkey [P] and select seperate by loose parts.
You can also seperate individual pieces by selection, I noticed that you have vertex groups for the different pieces, which would allow you to easily pick which parts to seperate.